The best advice he’d give his younger self is to not let his ego control him.

He noted that you never outgrow thinking you know more than you actually do.

If you can’t control it, your ego can destroy everything in your life.

That’s according to former Navy SEAL commanders Jocko Willink and Leif Babin, who teach this fundamental lesson through their leadership consulting firm Echelon Front.

Business Insider recently sat down with Willink to discuss his new book “Discipline Equals Freedom: Field Manual.” We asked him for the advice he would give his 20-year-old self, and he said it taps into this idea about ego.

While it may seem obvious that you know more about the world at age 30 than age 20, Willink said it’s important to realise that you’re never old enough to outgrow your ego — and it can make you susceptible to reckless decisions.

“If I went back to my 20-year-old self what I would tell my 20-year-old self is, ‘You don’t know anything,'” Willink said. “Because everyone when they’re young, they think they know what’s going on in the world and you don’t. And when I was 25, I thought that 20-year-old didn’t know anything but I thought my 25-year-old self knew everything. He didn’t know anything either. And when I was 30, the 25-year-old didn’t know anything. And then when I was 35, the 30-year-old didn’t know anything.”

Willink reflected on this in a previous interview with Business Insider. “When I get asked, you know, what makes somebody fail as a SEAL leader, 99.9% of the time it doesn’t have anything to do with their physical skills or their mental toughness,” he said. “What it has to do with is the fact that the person’s not humble enough to accept responsibility when things go wrong, accept that there might be better ways to do things, and they just have a closed mind. They can’t change.”

He noted that being ego-driven can, at times, be constructive. You want to be competitive, you want to prove yourself, Willink explained — but you need to realise that your opinions may not be the best available.

Willink said that this really crystallised for him when he began training young SEALS and saw how some were headstrong about beliefs that his experience taught him definitively were incorrect.

“And I would do my best to help them along that road and realise, ‘You’re not quite as smart as you think you are,'” Willink said.